EVB90620 Datasheet, PDF (2/39 Pages) Melexis Microelectronic Systems – High precision non-contact temperature measurements

MLX90620
16x4 IR array
General Description (continued)
The results of the infrared sensor measurements are stored in RAM:
16-bit result of IR measurement for each individual sensor (64 words)
16-bit result of PTAT sensor
Depending on the application, the external microcontroller can read the different RAM data and, based on the
calibration data stored in the EEPROM memory, compensate for difference between sensors to build up a
thermal image, or calculate the temperature at each spot of the imaged scene.
These constants are accessible by the user microcontroller through the I2C bus and have to be used for
external post processing of the thermal data. This post processing includes:
Ta calculation
Pixel offset cancelling
Pixel to pixel sensitivity difference compensation
Object emissivity compensation
Object temperature calculation
The result is an image with NETD better than 0.08K rms at 1Hz refresh rate.
The refresh rate of the array is programmable by means of register settings or directly via I2C command.
Changes of the refresh rate have a direct impact on the integration time and noise bandwidth (faster refresh
rate means higher noise level). The frame rate is programmable in the range 0,5Hz…512Hz and can be
changed to achieve the desired trade off between speed and accuracy.
The MLX90620 requires a single 3V supply (±0,6V) although the device is calibrated and performs
best at VDD=2.6V.
The MLX90620 is factory calibrated in wide temperature ranges:
-40…85˚C for the ambient temperature sensor
-50…300˚C for the object temperature.
Each pixel of the array measures the average temperature of all objects in its own Field Of View (called
nFOV).
It is very important for the application designer to understand that the accuracy of the
temperature measurement is very sensitive to the thermal equilibrium isothermal conditions (there
are no temperature differences across the sensor package). The accuracy of the thermometer can be
influenced by temperature differences in the package induced by causes like (among others): Hot
electronics behind the sensor, heaters/coolers behind or beside the sensor or by a hot/cold object
very close to the sensor that not only heats the sensing element in the thermometer but also the
thermometer package.
This effect is especially relevant for thermometers with a small FOV as the energy received by the
sensor from the object is reduced
3001090620
Rev 4.0
Page 2 of 40
Datasheet IR16x4
19 September 2012